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Grade 12 Advanced Functions, University Preparation (MHF4U)
B. Trigonometric Functions
24. 12AF.B3.3
24.1 Determining non-permissible values for trig expressions
Determining Non-Permissible Values for Trig Expressions
Find out when tangent, cotangent, secant, and cosecant are undefined, and learn a reliable method for finding non-permissible values.
What You'll Learn
Non-permissible values are the input angles that make a trig expression undefined, usually because they make a denominator equal to zero.
Tangent and secant are undefined wherever cosine equals zero, while cotangent and cosecant are undefined wherever sine equals zero.
To find non-permissible values, rewrite the expression using sine and cosine, set the denominator to zero, and solve that equation.
Solutions repeat every full rotation, so non-permissible values are written as a general pattern using plus n times 180 degrees or plus n times pi radians.
The same method applies to rational trig expressions with any denominator, not just the basic reciprocal functions.
What You'll Practice
1
Finding restrictions for fractions with sine and cosine in denominators
2
Solving equations like sin(x) = -1/2 and cos(x) = 0 using graphs
3
Writing general solutions with multiples of π for periodic restrictions
4
Identifying when expressions have no restrictions based on range analysis
Why This Matters
Understanding non-permissible values prevents undefined expressions in trigonometry, which is critical for calculus, physics, and engineering. This skill ensures you can safely simplify and evaluate complex trig expressions in advanced mathematics.
Before You Start — Make Sure You Can:
This Unit Includes
4 Video lessons
Practice exercises
Learning resources
Skills
Restrictions
Trigonometric Functions
Domain
General Solutions
Sine and Cosine
Reciprocal Functions
Undefined Expressions

ON Curriculum Aligned